FIELD OF THE INVENTION
This invention relates to a method for establishing a connection in a satellite system comprising at least one base station for transmitting and receiving electromagnetic signals, at least a first terminal for transmitting and receiving electromagnetic signals, at least a second terminal for receiving electromagnetic signals and at least one satellite with a transponder for receiving electromagnetic signals and for retransmitting the received signals, with the frequency of the retransmitted signals being shifted with respect to the received signals.
This invention further relates to a satellite system comprising at least one base station for transmitting and receiving electromagnetic signals, at least a first terminal for transmitting and receiving electromagnetic signals, at least a second terminal for receiving electromagnetic signals and at least one satellite with a transponder for receiving electromagnetic signals and for retransmitting the received signals, with the frequency of the retransmitted signals being shifted with respect to the received signals.
Such a satellite system is known per se. In these known satellite systems, such as the inmarsat satellite system, it is necessary to seek contact with the base station in order to file a request to establish a connection. For high-speed data links such as are used for digital video and digital audio connections, this requires special carrier waves operative in duplex mode via a separate narrow-band command channel. The first terminal desiring a connection with the second terminal should then first exchange information with the base station via the narrow-band channel, which information comprises, for instance, the identity of the first terminal and/or the identity of the second terminal as well as information relating to the connection to be established itself. When thus via the narrow-hand channel the necessary information has been exchanged with the base station, the first terminal can establish a wide-band connection. Such connection can then be made, for instance, with the second terminal. For the purpose of communication via the narrow-band channel and the wide-band connection, the first terminal will generally be provided with different transmitting and receiving systems. In particular, the second terminal is identical to the first terminal.
A disadvantage of such a system is that it is rather costly. This is caused by the fact that the terminals are provided with double transmission systems, whereby, as stated, the first transmission system is used for establishing a narrow-band connection with the base station, while the second transmission system is used for establishing a wide-band connection with another terminal or terminals. In the case of a satellite system these connections are established via the satellite. The object of the invention is to provide a method and a system that can be made of simpler, better and more efficient design.